what size carb

Posted By: coronetkid

what size carb - 09/28/10 01:38 AM

408 sbc
victor jr. intake
dart pro 1 heads
intake runner 200cc
exhaust runner 75cc
comb chamber 72cc
cam solid flat tappet .244/.252 duration
.520/.540 lift
SRP flat top pistons
comp ratio 10.5
1 3/4 hedman long tubes into x-pipe

what do you guys think?

Posted By: ScottSmith_Harms

Re: what size carb - 09/28/10 01:45 AM

Holley 950

Posted By: coronetkid

Re: what size carb - 09/28/10 09:25 PM

that big? really?

Posted By: gch

Re: what size carb - 09/29/10 12:16 AM

Gearing,stall,weight,etc would help for a race effort.Anything from a 750dp on up will work.
An 850 would probably take care of any street/strip effort.

Posted By: Moparzrule

Re: what size carb - 09/29/10 12:25 AM

MOE had an article on big carbs/small cubes.

http://editions.amospublishing.com/MPRE/default.aspx?d=20100701

Posted By: BSB67

Re: what size carb - 09/29/10 12:51 AM

Quote:

Holley 950

Its not 950 cfm. It has 1.375 venturi like a 750, with contoured body and 1.75 throttle bore. Throttle response of a 750, performance of an 850. Perfect for what you've got.

Posted By: Rustydog

Re: what size carb - 09/29/10 02:12 AM

General rule of thumb,
(Cubic inches X Max RPM) / 3456 = CFM

Posted By: Rustydog

Re: what size carb - 09/29/10 02:16 AM

I'd recommend 750 cfm
mechanical secondaries
jets 72 & 82
Don't over carburate with an 850 cfm

Posted By: RobX4406

Re: what size carb - 09/29/10 04:53 AM

Holley 950hp

That formula is only good if you want to under carb an engine IMO. Essenstially, it's good to arrive at the smallest carb you might want to use.

Posted By: superbyrd

Re: what size carb - 09/29/10 11:56 AM

i would agree on the 750 mechanical. the worst thing most people do is over carburate.....

Posted By: RobX4406

Re: what size carb - 09/29/10 03:41 PM

360 at 6500 says 688cfm using the formula.

Why is it that many go much faster with larger carbs and have used 1050 dominators doing so. My 360 is getting a 1050 so I must be crazy.

That formula is set up for a 1.5" pressure drop, IIRC. I don't know many that think a 1.5" drop is acceptable for a performance engine at full throttle. What adjustments have to be made to the formula for a 1", .5" or zero pressure drop? Something like a 23% increase going from 1.5" to 1.0" comes to mind.

Posted By: davenc

Re: what size carb - 09/29/10 06:17 PM

A 750CFM carb will only flow around 640CFM at 1.1" (if I did my math right). At 0.75", it will only flow 520CFM.

As I understand it, the issue with lower pressure drops is getting good fuel metering. Getting the carb right under such conditions is why some carb vendors can charge a premium.

If that 360 was spinning at 6500RPM, then a 800CFM carb at 1.1" would just meet its needs (assuming 100% VE at that RPM).